During the epitaxial production of semiconductor layers for optoelectronic components which are based on InGaAlN or InGaAlP, undesirable effects often occur even under optimized process conditions.
In epitaxial semiconductor layers composed of InGaAlN, indium-rich regions, so-called “clusters,” can form. High local strains arise in the region of the clusters, and can lead to formation of crystal defects which, as centers of non-radiative recombinations, reduce the efficiency of the LED. Even in the case of only a low degree of cluster formation, which does not lead to the formation of crystal defects, the efficiency of the LED can be reduced by an increased Auger recombination rate in the optically active layer due to a local charge carrier density increase in the region of the In clusters.
It has been established that the tendency toward formation of indium-rich regions can be reduced by the use of high growth temperatures, as a result of which, however, incorporation of indium into the epitaxially produced layers is also impaired. During epitaxial production of InAlGaN semiconductor layers by MOVPE (Metal Organic Vapor Phase Epitaxy), formation of clusters can also be reduced by a comparatively high reactor pressure of more than 800 mbar. However, this leads to a great increase in undesirable prior reactions of the process gases, which contain, for example, NH3 or organometallic compounds such as TMGa, TMAl or TMIn, as a result of which formation of nanoparticles and, hence, defects in the semiconductor layer can occur. Reduction of such prior reactions by spatial and temporal separation of the feed of the source materials responsible for the prior reactions is also suitable only to a limited extent owing to associated restrictions of the growth parameters, in particular of the growth rate, and also more stringent requirements made of the epitaxy apparatus and high costs associated therewith.
Formation of indium clusters can also be reduced by using a high ratio of the group V material to the group III materials, in particular by a high supply of NH3 in the gas phase. However, in this case, too, the prior reactions of the process gases increase and the costs for provision of NH3 increase.
During epitaxial production of semiconductor layers for InGaAlP-based LEDs it can be observed that the material of the epitaxial layers deposits in an ordered fashion such that regions having a more or less distinct alternating arrangement of the group III atoms arise. This effect is also known as “ordering.” These regions are separated from one another by grain boundaries which can reduce the efficiency in the active layer of the LED as centers of non-radiative recombinations. In the case of LEDs, the active layer is generally surrounded by barrier layers which have a larger electronic band gap than the active layer and thus lead to charge carrier confinement in the active layer. It has been observed that, as a result of the ordering, a reduction of the band gap of the semiconductor material occurs which adversely affects the function of the barrier layers and in this way can lead to an increase in leakage currents and thus to a reduction of efficiency of the LED.
The ordering can be at least partly reduced by using high growth temperatures, but an undesired diffusion of dopants in the epitaxial layers is also intensified as a result.
It could therefore be helpful to provide an optoelectronic semiconductor component based on an indium-containing phosphide compound semiconductor or nitride compound semiconductor which has an increased efficiency. In particular, it could be helpful to reduce the above-described disadvantageous effects which adversely affect efficiency.